Year 8 Science · Unit 3 · Lesson 5
Challenge Worksheet
Learning Goals
Design a mini-experiment
A science class wants to test: "Does photosynthesis in aquatic plants produce oxygen as a product of a chemical reaction?" They have access to water plants (Elodea australis, a native Australian aquatic plant), light sources, limewater, a glowing splint, and beakers. Plan their investigation using what you know about evidence of chemical reactions and the physical vs chemical change framework.
| What we are testing (research question in your own words) | |
| What we will change (independent variable) | |
| What we will keep the same (controlled variables — list 3) | |
| What we will measure or observe (dependent variable) | |
| How we will test the gas produced (method + expected result) | |
| My prediction (using lessons 1–4 vocabulary) | |
| How I would know if my prediction is wrong | |
| One limitation of this experiment |
1. Photosynthesis is a chemical change. Using lessons 1–4, write a complete justification: state the reactants and products, identify at least two observable pieces of evidence, and use particle-level language to explain what distinguishes it from a physical change.
2. A student claims: "Photosynthesis must be physical because the water and CO₂ are still there — they just changed form inside the plant." Critique this claim: explain why access to the starting materials again does not make the process physical, and what the particle-level difference actually is.
Wrap Up
In one sentence, what was the main idea of this unit?